The present invention relates to a wide angle lens system and a camera provided with the wide angle lens system.
In recent years, there has been increased demand for a reduction in size or thickness of a digital camera. Further, a demand for a reduction in size or thickness and cost saving is also high with respect to an imaging optical system mounted in a digital camera. In order to meet these demands, an imaging optical system in which optical elements such as a prism used to bend a light path halfway are arranged has come into practical use while the number of the optical elements is reduced.
Further, in recent years, there has also been an increased demand for an imaging optical system having a wide field angle or an imaging optical system which is bright even if its F number is small in order to increase added value of a product while achieving excellent correction of aberration to cope with an increase in the number of pixels of a solid state imaging element such as a CCD.
Japanese Patent Laid-Open Publication No. 2004-53993, Japanese Patent Laid-Open Publication No. 2003-302575, Japanese Patent Laid-Open Publication No. 2003-98430 and Japanese Patent Laid-Open Publication No. 2000-292692 each disclose an imaging optical system in which light path bending members and others such as a negative lens having a negative refractive power, a prism or the like are arranged in order from an object side.
Japanese Patent Laid-Open Publication No. 2004-53993 and Japanese Patent Laid-Open Publication No. 2003-302575 disclose a zoom lens system including, in order from an object side, a first lens group having an overall negative refractive power, a second lens group having an overall positive refractive power, and a third lens group having an overall positive refractive power. Japanese Patent Laid-Open Publication No. 2004-53993, Japanese Patent Laid-Open Publication No. 2003-302575 disclose the zoom lens system which has the reduced number of optical elements and corrects an aberration while decreasing a size thereof as a structure in which the first lens group includes a negative lens and a light path bending member in order from the object side.
However, in the zoom lens system disclosed in Japanese Patent Laid-Open Publication No. 2004-53993 or Japanese Patent Laid-Open Publication No. 2003-302575, a distance between the first lens group and an aperture is long on a wide angle side in order to configure the zoom lens system. Therefore, in order to realize a so-called super wide angle, the light path bending member or the negative lens arranged on the object side apart from the light path bending member must be considerably increased in size. Furthermore, a half field angle of the zoom lens system disclosed in Japanese Patent Laid-Open Publication No. 2004-53993 or Japanese Patent Laid-Open Publication No. 2003-302575, is approximately 30 degrees to 32 degrees, and configuring a super wide angle lens system having a half field angle of 40 degrees to 50 degrees is not considered.
Therefore, Japanese Patent Laid-Open Publication No. 2004-53993 or Japanese Patent Laid-Open Publication No. 2003-302575, do not disclose effective means for correcting various aberrations such as a coma aberration outside an optical axis which becomes a problem when configuring a super wide angle lens system having a half field angle of 40 degrees to 50 degrees.
Moreover, Japanese Patent Laid-Open Publication No. 2003-98430 discloses a fixed focus lens constituted of a negative lens, a light path bending member, an aperture, a positive lens system and a cemented lens which is obtained by cementing the positive lens and the negative lens in order from an object side.
However, the fixed focus lens system disclosed in Japanese Patent Laid-Open Publication No. 2003-98430 has a configuration in which the aperture is arranged immediately after an exit surface of the light path bending member. Therefore, correction of an aberration of a light beam which enters from a wide field angle is difficult when the fixed focus lens system disclosed in Japanese Patent Laid-Open Publication No. 2003-98430 is used to constitute a super wide angle lens system, and hence excellent image forming performance is hardly obtained.
Additionally, Japanese Patent Laid-Open Publication No. 2000-292692 discloses a technique which forms at least one of an incidence surface and a reflecting surface into a curved surface as a light path bending member, thereby reducing a size.
However, in the case of the light path bending member disclosed in Japanese Patent Laid-Open Publication No. 2000-292692, manufacture of an optical element unit is difficult compared with a regular prism whose light ray transmitting surfaces or reflecting surfaces are all flat surfaces. Further, since optical axis matching when incorporating such an optical element in an optical system is also very difficult, stably obtaining high performance is difficult in manufacture.
Furthermore, a half field angle of the lens system disclosed in Japanese Patent Laid-Open Publication No. 2003-98430 or Japanese Patent Laid-Open Publication No. 2000-292692 is approximately 30 degrees to 36 degrees, and these references do not disclose effective means for correcting various aberrations such as a coma aberration outside an optical axis which becomes a problem when constituting a super wide angle lens system whose half field angle is 40 degrees to 50 degrees.